Originally Posted by scorkey
You can either call and have the infant added to your PNR ahead of time or just notify them at the airport.
The infant is not issued a separate boarding pass, but a sticker is affixed to your boarding pass noting your infant as a lap child. This is mainly for headcount purposes. On a rare occassion, UA will print a boarding card for an infant and staple it to yours (I think they did it for us because they were out of the stickers).
In '01-'02 on all my UA flights a separate BP was printed for infant. Yes you need to inform them, but it can be done at check-in at the airport, or even at the gate. But it must be done before boarding so they can get the count.